1. Field of the Invention
The present invention relates to compositions of matter which enhance the stability of solid-in-liquid dispersions. More specifically, the invention relates to surfactant systems for relatively lipophilic and/or hydrophobic materials, such as active antimicrobial materials, dispersed in lipophobic and/or hydrophilic liquids.
2. Description of Related Art
Water-based antimicrobial products are in great demand because, among other reasons, various governmental bodies have begun to restrict the use of solvents which contain volatile organic carbon (VOC). These restrictions are reportedly intended to enhance human health by improving the environment. As a result, many industries are switching from organic solvents to water-based solvents, which are inherently more susceptible to biological attack. More and better antimicrobial products are needed to protect the water-based solvents, and it is widely preferred that the antimicrobial products themselves are now also water-based and free of organic solvents.
To fulfill this need, concentrated products with relatively higher concentrations of antimicrobially active materials (hereinafter referred to “actives”) are favored by the antimicrobial product industry because concentrated products are easier to transport and store. However, many desirable actives are lipophilic and/or hydrophobic to the extent they do not easily dissolve in water-based liquids and are better combined in the form of solid-in liquid dispersions or liquid-in-liquid emulsions. Consequently, the physical stability of water-based dispersions containing active (hereinafter referred to as “active dispersions”) is important.
Some otherwise desirable active dispersions are impractical because they exhibit phase separation over time. Other active dispersions simply cannot be prepared in the sought-after concentrations using currently available methods. This is frequently the case when a number of actives are combined in an attempt to formulate a single product which consumers may find more efficient and convenient to use, as compared to products having only one active. Concentrated water-based dispersions including a combination of actives are at the cutting edge of antimicrobial formulation development.
In order to meet the demand for concentrated water-based dispersions, some formulators have added pH-adjusting agents. Assuming that these pH-adjusting agents actually promote physical stability, they cannot be considered a final solution, because the change in pH which they bring about can negatively impact the performance of the actives.
U.S. Pat. No. 6,306,413, issued to Payne, describes a stable aqueous formulation comprising from 5 to 30% by weight microbiologically active agent containing at least 50% BIT, from 1 to 4% dispersant and from 0.1 to 0.5% by weight xanthan gum. The formulation is said to be substantially free from organic solvents. Dispersants of the '413 patent reportedly include condensates of ethylene oxide or propylene oxide (including block co-polymers of ethylene oxide and propylene oxide), sodium lignin sulphonate, the sodium salt of naphthalene sulphonic acid/formaldehyde condensates and mixtures thereof. However, as demonstrated below, the present inventors have found that the sodium lignin sulphonate-containing formulations of the '413 patent exhibit undesirably high viscosities at relatively higher concentrations.
Japanese unexamined application JP 2-268900, assigned to Kurita Seisakusho K.K. and Kurita Water Industries Ltd., describes a slurry-form deodorizing agent for use in preventing foul smells arising from sludge. The deodorizing agent of the '900 application reportedly comprises 5-70 wt % of a deodorant such as 1,2-benzisothiazol-3(2H)-one or methylene bis-thiocyanate, 0.1-10 wt % xanthan gum, 0.1-0.5 wt % polyacrylamide which optionally may be partially hydrolyzed, and water. However, as demonstrated below, the polyacrylamide-containing formulations of the '900 patent exhibit undesirably high viscosities at relatively higher concentrations.
World Intellectual Property Organization patent application no. PCT/EP04/10114, assigned to Bayer CropScience LP, describes suspension concentrates comprising a) at least one active compound, solid at room temperature, from the group of the azoles and/or the strobilurins, b) at least one penetration enhancer from the group of the alkanolethoxylates, c) at least one dispersant from the group of the polymers of methyl 2-methyl-2-propenoate and alpha-(2-methyl-1-oxo-2-propenyl)-omega-methoxypoly-(oxy-1,2-ethanediyl), the tristyrylphenolethoxylates and/or the propylene oxide/ethylene oxide block copolymers having molecular weights between 8000 and 10 000, d) water and also e) additives, if appropriate. However, the alkanolethoxylates required by the '114 application are organic solvents and, therefore, inappropriate for use in organic solvent free, water-based antimicrobial products.
Previous researchers have devoted much effort to developing better surfactant systems and improved antimicrobial formulations. However, a need still exists for a surfactant system which stabilizes relatively concentrated, water-based dispersions of combined actives over a practical viscosity range and at a pH which is approximately neutral. New dispersions which include the surfactant system should be essentially free of organic solvents, should be effective for a number of proven active antimicrobial materials, and should not discolor other products to which they may be added or applied.